


The Subtlest Beast

by tiggeryumyum



Series: Age Swap AUs [1]
Category: Haikyuu!!
Genre: Age Swap, M/M, Minor Iwaizumi Hajime/Oikawa Tooru
Language: English
Status: Completed
Published: 2018-07-29
Updated: 2018-07-29
Packaged: 2019-06-18 11:15:37
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,694
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15484563
Author URL: https://archiveofourown.org/users/tiggeryumyum/pseuds/tiggeryumyum
Summary: First year Oikawa is determined to replace third year Kageyama as Seijoh's regular setter.(AU where Oikawa and Kageyama's ages are swapped)





	The Subtlest Beast

Two years ago, in junior high, Iwaizumi warned Kageyama, "If you pull that shit in a real game, I'm going to punch you."

And then Kageyama _pulled that shit_ in a real game, and got punched.

They were both suspended the rest of the season (all forty-five minutes of it), and it was embarrassing for them, and Kitagawa Daiichi, and their coaches, and probably their mothers, but Oikawa didn't hear anything about that, personally. 

Oikawa did hear the two of them later that night, shouting in the gym, after everyone else had left. It was the same argument Oikawa heard over and over again throughout the last year, but there was something new about it that night, a sharper edge. Dangerous. 

"If you wanted to win, you'd be faster – "

"If _you_ wanted to win, you'd toss something a spiker can actually hit!!!" Iwaizumi shouts.

Oikawa peered silently from the door to the lockers, wide eyed, watching his senpai glare at each other in furious standstill. 

Oikawa's family is friends with Iwaizumi's family, and he knows Iwaizumi very well. Oikawa likes Iwaizumi's attention, and he feels happy in a way that's hard to name when he sees Iwaizumi mad at someone else, while Oikawa stays in his good graces. 

It's exciting, thrilling, to see him angry like _this_. He seems adult, and wild, unstoppable.

Oikawa darts quickly to the side when Iwaizumi storms past the lockers, grunting out a quick apology to Oikawa for startling him as he leaves, not stopping to change.

It's the last time either Kageyama or Iwaizumi show up to practice at Kitagawa Daiichi. There's a rumor started that they were banned after the fight, but Oikawa knows it's a lie. He knows it's because if they see each other again, there will be a second fight, even worse than the first.

Now Oikawa is in his first year at high school. 

He was invited to attend Aoba Johsai and accepted, of course. He knows, from a very reliable resource, that Aoba Johsai is in desperate need of a setter who can get along with a team. This is Oikawa's specialty.

"You're still miles away from being as good as Kageyama-san, though," Kindaichi says. "No way you're gonna set this year." 

"It doesn't matter how good you are technically if you don't mesh with your team," Oikawa says.

"He meshed well enough to get Seijoh to nationals," Kunimi points out, in his eternally bored voice. 

"For _one game_ ," Oikawa says, and starts eating his lunch, then puts it down a second later. "And Kageyama-san isn't _that_ much better."

Kunimi and Kindaichi both stare, disbelieving. 

Oikawa feels his face heat, going back to his lunch. "Whatever."

Kageyama _is_ that much better, but he's not perfect. 

Or, he is perfect, but not perfect for Aoba Johsai. 

Iwaizumi hasn't told him that _exactly_ , but every time Oikawa's family has been invited over to Iwaizumi's home the last two years, he and Oikawa would practice tosses in the backyard, and Iwaizumi would complain about how Kageyama is a _know-it-all tyrant_ , and how Iwaizumi is looking forward to playing with Oikawa on a real team again. 

Oikawa plans to bring out the best in Seijoh, and prove his worth. He's going to usurp the regular setter position, and send tosses to ace Iwaizumi, and together they'll bring down Shiratorizawa, and make it to nationals. They'll share triumphant victory on the court, and Iwaizumi will look at him with respect, then vow that he'll be waiting for him at university so they can play together again – 

"Your serve needs work."

Oikawa blinks, his daydreams popped, flying wildly away as they deflate, leaving him alone with Kageyama-san in the gym of Aoba Johsai.

"What?"

"I saw your serve in practice, and it needs work."

Oikawa is always, unfailingly, polite to his senpai. He can literally feel the smile on his face shaking slightly from rage, though.

"Really, Kageyama-san?"

"You're hurrying into the jump," Kageyama says. "You need to work on the walk up."

Oikawa's smile grows wider, and angrier. Thankfully, Kageyama doesn't seem to notice. If a person had to compare Kageyama's serve and Oikawa's serve (and Oikawa has) Kageyama's serves are cautious. They're slow, he uses the entire six seconds to walk up. Oikawa is faster. His power comes from the momentum of his jump. He's not going to suddenly slow down a serve he's been working on since junior high just to match what Kageyama does, because Kageyama thinks _his_ is the right way to do it. 

"I think it's a formidable weapon as is," Oikawa says, staying calm, voice light. "I got five service aces in my last sports meet – "

"And how many outs?" Kageyama asks. Oikawa pinches his mouth shut. More than five. "Any pitch server on this team is going to need a better accuracy rate than that."

 _Pitch server._ The words echo in Oikawa's head, and he feels anger ballooning out of control. Oikawa plans to be doing more than _pitch serving_.

"Stop picking on the first years."

Iwaizumi comes up from behind and gives Kageyama a rough, hardy shove. Kageyama stumbles, then frowns, rubbing at his shoulder.

The heat of Oikawa's anger is immediately cooled to almost nothing, biting his lip in delight.

"Oikawa's serve is fine, he just needs to work on his control," Iwaizumi says. 

"If he needs to work on his control, then it's not fine."

"You know what I meant," Iwaizumi says, crossing his arms. "And what room do you have to talk anyway, what did your serve look like in your first year?"

"It was strong!"

"Right, I remember you serving at least half out each game," Iwaizumi says. Kageyama huffs.

Wait. 

Oikawa watches the two of them, eyes narrowing.

There's warmth, there. A degree of teasing. On both sides.

This isn't the furious circling he remembered from junior high. They've moved beyond that. _He's a tyrant_ , Oikawa remembers Iwaizumi saying in his memory, but now, with this new scene playing out ahead of him – he realizes that was said with a degree of exasperated fondness. 

Kageyama is getting flustered and defensive, and Iwaizumi is enjoying it. 

Anger, colder than he's ever felt, settles around Oikawa, draping around his shoulders. He takes a few steps back from the two of them as they continue, and neither notice.

Oikawa goes back to practicing his serve.

~

"Oikawa, leave that to Kindaichi," Kageyama says, crossing his arms from the side of the court while Oikawa helps take down the net. "We're going to work on your serve."

"Sorry, Kageyama-san, but I can't stay late today," Oikawa says.

"You couldn't yesterday either."

"Bad luck, right??" Oikawa says, and flashes him a peace sign. 

Iwaizumi watches with one eyebrow raised.

Later, when Oikawa is practicing in the neighborhood park, Iwaizumi shows up. Oikawa tosses the ball his way as a form of greeting. Silently, Iwaizumi receives, sending it back.

They do this for a minute or two, until Iwaizumi clears his throat.

"It couldn't hurt to listen to him," Iwaizumi says. "Eight times out of ten he gets a service ace. He knows what he's doing."

"I want to develop my serve on my own," Oikawa says. "Not copy Kageyama-san's. He's such – a _tyrant_."

He watches Iwaizumi carefully to see his reaction. When Iwaizumi smirks, amused, Oikawa feels his anger grow.

"He is," Iwaizumi says. "But his serve is the best I've ever seen."

The best. Oikawa's hands, clasped together for the receive, tighten. Silently, furiously, he vows to himself that he'll hear Iwaizumi say that about himself, one day.

"Like I said," Iwaizumi shrugs, oblivious. "Couldn't hurt."

~

"Your first step is weak," Kageyama says. He's cornering Oikawa now, at the end of practice, instead of attempting to lure him in later, not giving him any choice about it.

Oikawa nods, and keeps his face as respectful as possible. When Kageyama takes a step back, obviously expecting Oikawa to make another attempt at a serve, Oikawa bows and thanks him for the extra tips, then leaves for the locker room.

Once the door shuts behind him, Oikawa glares, slamming his gym bag down on the bench, and he hears a snicker. He's annoyed until he looks up and sees Hanamaki and Matsukawa, two third years.

"Ah. Hello," he says, politely.

"Don't let him get to you," Hanamaki says. "He's always been like that."

"To be fair," Matsukawa says. "He has gotten worse since the national team."

"Worse?" Oikawa asks.

"You know, he learned all those practice drills for professionals, and now he wants us to do them," Hanamaki says, shaking his hand dismissively. "I wanna win as bad as anyone but – damn, it's not _that_ serious. I think he forgets we're a bunch of high school students."

"That's our tyrant," Matsukawa says with bland sarcasm. Still that exasperated affection, though. "And he's not exactly the smartest guy in the world to begin with, so you have to be straightforward."

"Just let him know you're not as serious as he is if you want him to back off," Hanamaki says. "He will."

It's kind advice, and drives through Oikawa's gut like a pickaxe. 

Oikawa _is_ that serious. 

Perhaps Kageyama is actually the only other person on this team that matches Oikawa's level of seriousness, like some kind of Greek tragedy. Iwaizumi wants to win, but he's too pragmatic to let it grow wild and crazy inside him like it does in Oikawa, and in Kageyama. 

But Oikawa is pragmatic enough that he's not surprised when the coach announces the line up for the tournament.

Kageyama is the starting setter. None of the first years make a regular position, and Oikawa is regulated to pitch serving. He's annoyed, but the entire team has molded and shaped around Kageyama's tosses. He's not the captain but he might as well be, from how his direction drives the team. The sheer amount of work it would take to develop a new team from scratch with Oikawa at the heart of it makes the coach's decision understandable.

Oikawa will just make as many service aces as possible, _with his own serve_. His own style.

"Twenty-five serve aces in a row?" Iwaizumi asks, amused, the night before inter-high begins.

"That's the plan," Oikawa says, grinning. 

"Well try to leave some fun for the rest of us," Iwaizumi says.

"Twenty-four then," Oikawa allows, and Iwaizumi chuckles, voice a low rumble that makes Oikawa feel warm, all the way back home.

~

Not a single service ace.

Oikawa stares down at his lap on the bus ride back, eyes watering from pure rage. No one sits beside him, and this is a relief. If anyone tried to touch him or comfort him right now, he might throw a punch.

How? How could he have done so poorly?

The coach kept giving him chances, too, putting him in twice against Karasuno. Oikawa's chest hitches in humiliation, remembering the captain in the back row, scooping up Oikawa's serves like they were _nothing_. Easy. 

Once back at Aoba Johsai's gym, the coach gives them a short, but upbeat pep talk back at the gym. They made it all the way to the semi-finals, and it was a good run. Everyone gave their all, and Oikawa is taking the loss hardest by far, feeling so angry with himself he's become hollow with it, a shell around his burning, smoldering insides.

"We'll start getting ready for Spring high tomorrow, alright?" Iwaizumi says softly, squeezing Oikawa's shoulder as he passes. It's the only thing anyone could've said. Oikawa quickly wipes his face and nods. 

"Right."

Everyone else seems to have this optimistic attitude. _One chance left_ , after all. There's still spring. 

Oikawa wanted to win _this_ , though, and he is not satisfied with the idea that there will be other chances. 

There's one other person sharing the same frustration, not allowing himself to be distracted from the failures of today by future promises. 

Kageyama stands in the gym with his arms crossed. 

"Oikawa."

"Kageyama-san," Oikawa says. His voice shakes. _Keep away, don't, not now, not now,_ but Kageyama doesn't hear the silent plea. 

"You need to work on your form," he says. "If you have a weak first step, there's no foundation."

Oikawa swallows, and tries to compose himself. "I'll keep that in mind, Kageyama-san!" he forces out with false, saccharine pep.

Kageyama tilts his head to the side, like he thinks he's being mocked. "Your sloppy serves cost us the win today."

Oikawa closes his eyes.

"You've got the talent to help this team but you wasted it, and it slowed us down – "

" _No one likes you_ ," Oikawa shouts. It echoes for a moment, and Oikawa takes a wild, desperate breath, doesn't open his eyes, and keeps going. "They put up with you, but everyone – Hanamaki-san, Matsukawa-san, Iwaizumi-san – they think you're a _tyrant_. They think you're an idiot, they think you're awful, they said it themselves!! They hate how you boss them around!! No one wants to be around you!!"

Oikawa takes another wild breath and forces himself to open his eyes.

Kageyama stands there. His expression isn't that different from normal. It's small things, the slight widening of his eyes, his mouth frozen, open just a crack. He blinks and this panics Oikawa. 

He grabs his bag and runs out of the gym, not strong enough to endure whatever's going to come next.

~

Outside of blunt volleyball talk, Kageyama's usually pretty quiet, but he doesn't talk to anyone the next day at practice. He keeps to himself in the corner of the gym, doing a series of brutal exercise routines Oikawa's never seen before.

"They're called pukers," Hanamaki says.

"What is?" Kindaichi asks.

"It's this routine he learned from the national team," Hanamaki says. The group of them stands and watches Kageyama, across the gym, push up, squat, jump, roll, then drop back to a push up again. Just watching makes Oikawa's abs throb in sympathy.

"He's taking interhigh pretty hard, then," Matsukawa sighs, rubbing at the back of his head.

"Hey!" Iwaizumi says, tossing the ball at Matsukawa, forcing him to catch it before it can bounce off his head. "It's our practice, too."

The group stops their gawking, going back to their own routines, but Oikawa and Kindaichi watch a beat longer. 

"He's so intense," Kindaichi says, sounding both awed and horrified.

"Yeah," Oikawa says, shifting away a little guiltily. When Kageyama passes by him at the end of practice on the way to the locker room, Oikawa flinches, bracing for some kind of confrontation, but Kageyama says nothing, doesn't even look his way.

"Just let him be," Iwaizumi says, apparently catching Oikawa's worried expression. "He'll be back to normal soon."

But by the end of the week he's still keeping to himself. 

Oikawa has gone from guilty to annoyed – really, Kageyama is a third year, he shouldn't take the words of his kohai so seriously, he should stand on his own, what sort of right does he have to be so good, and so aggressive, so in Oikawa's face all the time, and then immediately fold the second Oikawa says something mean?? It's not fair. So maybe he does still feel guilty, even guiltier, actually.

He doesn't want Kageyama to tell anyone what he said, but at this point he'd bear it, he'd apologize and everything, if only the weird mood cast over the gym would leave. 

In this sense it's a relief when he passes by the locker room and hears the third years voices, impatient and loud. They're worried, and it's showing itself as annoyance, too.

"Get over it already, Tobio! We lost, we'll have another chance in a few months – "

"I'm not upset about interhigh," Kageyama's voice says, quiet and angry.

The locker room goes quiet. 

"Oh?"

"Then what's this whole Mr. Moody routine??"

"You told me," Kageyama is saying, voice tight. Stilted. "That if I was getting bad. You'd say something."

"Yeah?" Matsukawa says, confused. 

"Why wouldn't we?"

"You think you've gotten bad again?" Iwaizumi asks. This tone reminds Oikawa of the fight he overheard between them, back in junior high. Not because of any anger, but because of the seriousness of the tone. Iwaizumi feels adult. Dangerous. Unstoppable. And instead of feeling thrilled by it, Oikawa feels impossibly small and young and immature, decades away from the group.

Kageyama doesn't answer, but after a moment of quiet, the four of them start gathering their things.

The door jumps open so quickly, Oikawa doesn't have time to pretend to be doing anything other than what he was.

"Hey – oh. Oikawa," Iwaizumi blinks in surprise to see Oikawa standing there, cutting his shout short. "We're ending practice early. Let the others know, alright?"

"Alright," Oikawa says.

Iwaizumi stares at him for another second, and Oikawa can see him wondering, what exactly Oikawa was doing, what he overheard. Oikawa smiles weakly. It's nothing like his 100 watt, _who, me??_ grin.

Iwaizumi shakes his head.

"See you tomorrow, Oikawa."

~

Oikawa goes to bed nervous, wakes up nervous, spends all of his classes nervous, a cold chill of worry settling over him each time he tries to imagine how the third years conversation went. 

Iwaizumi isn't the type to stand for that kind of behavior, and the idea of Iwaizumi looking at Oikawa with distaste – while standing at Kageyama's side as a support – Oikawa is nearly in a cold sweat as he walks toward the gym.

Nothing happens.

Kageyama is back to his normal self, barking at second years to pick up the pace in setting up the gym. He looks up when Oikawa opens the door, but doesn't say anything, focusing back on the second years.

Iwaizumi, also, says nothing out of the ordinary, treating Oikawa as he always has, kind and encouraging. Slowly, Oikawa eases into practice again, unable to believe his luck.

But maybe it's not that surprising? Kageyama isn't the best communicator, maybe it didn't occur to him to say why he was suddenly worried. Maybe they hadn't thought to ask… ?

Later, in the corner of the gym, during stretches, Oikawa gets his answer. 

"Hey, Oikawa," Hanamaki says, walking up to squat beside him. He doesn't seem angry. "Like we talked about earlier – you just have to tell Kageyama to back off, and he will. He won't be bothering you anymore, alright?"

"Ah," Oikawa says. He nods once. "Thanks."

Hanamaki smiles, gives him a pat on the back. "You've got a great serve. Don't let him get into your head."

"Thank you, Hanamaki-san," Oikawa says. He runs this over in his mind. It makes sense. How the conversation went. Kageyama assumed he was at fault, relayed he was at fault, and the others corrected his behavior.

A bratty voice in Oikawa's head wants to agree. Kageyama _was_ at fault, wasn't he? He was saying things Oikawa didn't want to hear, and wouldn't leave him alone! 

But Oikawa quickly waves it away, annoyed by its presence.

~

He isn't trying to make a habit of spying on the third years, but the locker room is right there, and they don't talk quietly. When he hears their voices and what is obviously a very candid conversation about what they think of the new first years, of course he's going to listen in.

"Kindaichi's improving fast. I think he might actually be made a regular for Spring high."

"Kunimi's moving along, too."

"Not as quick as he could be," Hanamaki says.

"Talented but lazy," Iwaizumi says.

"So's that Oikawa kid." 

"He's not lazy," Kageyama says.

There's a beat of surprise, both in the room and in Oikawa. His mind spins at this, this person he spewed those hateful words at, defending his name when he could just keep silent or even join in. Looking back at his behavior, it would be the easiest thing for Kageyama to assume, even, that Oikawa is lazy, bratty, unmotivated.

"Kageyama," one of them sighs. "You can't ride the first years because _you think_ they can do better. They've got more on their plate than volleyball, not everyone is going to play in college – "

"I know that," Kageyama mutters, sounding defensive. This is obviously a conversation they've had many times before.

"Then why are you so obsessed with Oikawa's serve? It's _just fine_ for a first year." 

"It's better than yours was at that age."

"Because," Kageyama says. Oikawa can't see his face but he can hear the strain in his voice as he tries to put this to words. "He wants it. He wants to win. And he could help us win if it was better."

"It could be better," Iwaizumi agrees, softly, like he knows it's a betrayal to Oikawa to say this. "But that's not something you can force."

"I wonder if it's just a bad attitude," Matsukawa muses. "If he can't set, he thinks pitch serving is below him, or something?"

This lands too close to home. Oikawa scrunches his nose, embarrassed, and annoyed, too, but mostly with himself for being so transparent. Hearing it in those terms makes Oikawa feel younger, again, in a far more pathetic way than before.

"He wants to win, though," Kageyama says. He sounds a little confused. 

Kageyama is a tyrant, he's prideful and stubborn, but in this way, he is selfless. This – all this immature flotsam Oikawa allowed to clutter his path would never be a conflict for Kageyama, and knowing that Oikawa wants to win as badly as he does, he literally cannot conceive what could possibly be standing in the way of that. What Oikawa could possibly value more. 

The conversation moves on to the other players and Oikawa sits there long after they've left, feeling oddly humbled. 

~

"Kageyama-san."

At the end of practice, Kageyama sits on the bleachers, a whiteboard in his lap. He looks up. He's surprised and it's actually only now, at this moment, that Oikawa sees that his dark eyes are a shade of blue.

Dropping his gaze, Oikawa runs his fingers across the tread of the ball in his hand, feeling sheepish.

"I was wondering," he sighs shakily. _Take the plunge, Tooru._ "If you could show me your serve."


End file.
